The present application relates generally to fuel sensors for vehicles and, more particularly, to a sealed fuel level sensor for a vehicle.
It is known to provide a fuel level sensor in a fuel tank of a vehicle to sense or indicate a level of fuel in the fuel tank. Examples of such fuel level sensors are disclosed in U.S. Pat. No. 5,746,088, U.S. Pat. No. 6,021,668, and U.S. Pat. No. 6,681,628. Typically, the fuel level sensor includes a ceramic resistor card operatively connected to structure for a fuel module and a wiper assembly pivotally connected to the structure for engaging the resistor card. The wiper assembly has one end connected to a float arm and a float member to rotate the wiper assembly relatively to the resistor card based on a level of fuel in the fuel tank.
Thick film ceramic fuel level sensors are open and exposed to fuel in the fuel tank. These fuel level sensors typically employ silver (Ag) based conductive inks (Ag, Pd, Pt) and high content Ag contacts (Paliney6, Ag/Ni). These materials function in fuels that contain moderate sulfur levels or that are low in alcohol content. These materials have also allowed manufacturers to produce a cost effective fuel level sensor.
Fuel level sensors that are open and exposed to fuels have always been susceptible to solid contaminates such as, for example, sand, which can cause the sensor output to produce opens. As the sulfur level in fuels is reduced, smaller, more reactive compounds are more likely to be left behind in the fuel. Sulfination is a chemical reaction between Ag and sulfur. Natural aging of the ink/contact interfaces of the fuel level sensor exposes the silver in these components to sulfurs, producing a thin lacquer contamination. Silver based fuel level sensors produce opens or a shift in resistance when exposed to this extremely reactive fuel.
Also, as refineries introduce fuels with higher levels of alcohol, silver based fuel level sensors that are open or exposed to this fuel are more susceptible to plating, galvanic, or dendritic growth. Galvanic growth is a plating process which forms an insulating layer between the contacts and a working surface of the conductive ink, no matter if the materials are Ag based or Noble metals. Given enough powered exposure time, the output of the fuel level sensor will produce an open. Dendritic growth is a silver migration that will short out segments of the resistor of the fuel level sensor.
The inventors herein have recognized a need for an improved fuel level sensor that provides a sealing mechanism for a fuel level sensor assembly that is dimensionally stable when exposed to the harsh chemicals of fuel formulations and also permits free rotation of the float arm to thereby limit exposure of a variable resistor assembly in the fuel sensor to chemicals found in fuels to reduce particulate contamination, sulfination, and dendritic growth.